Seymour Duncan Convertible 100 Input

[bobloblaws]

The components are the same on both of my amps. I'm confident the 4.7M resistors and the following input wiring scheme have not been tampered with because I bought one of my amps from the original owner and he was definitely not tech savvy.

The upper input: Tip is grounded if no jack is inserted. This ground disables both the upper and lower input if no jack is inserted.
The lower input: Tip is connected to the tip of the upper input via a 100K resistor (brown:black:yellow). Lower input is grounded if no jack is inserted in upper input.

Sorry for my slow reply. I was expecting an email informing me if there was any new thread activity.
Graham

Awesome, thanks for this, Graham.

[drewl]

Holy *&^%, who designed this insane beast?

Got one in and figured out a few things you guys described here. These sound pretty cool, but my god, let someone with experience design the box.
A nightmare to service, stuff all over the place, yikes!

[pslebow]

Does anyone have the main printed circuit board layout for the Seymour Duncan Convertible 100W amp?

[bobloblaws]

Does anyone have the main printed circuit board layout for the Seymour Duncan Convertible 100W amp?

I don't know about a layout, but there is a schematic here:

https://el34world.com/charts/Schemat...rtible_100.pdf

[pslebow]

Yes, thanks. I do have the schematics. Problem is the the side of printed circuit board with the traces is inaccessible. To tie a component to the schematic is very time consuming using an ohm meter. I wanted to find the input point to the phase inverter V2 input, for instance. Turned out to be 6 inches from the tube pin after much trial and error hunting. I contacted SD but they claim they don't have the layouts anymore. Hard to believe.
But thanks.

[GrahamPearson]

I have a bunch of files: schematics, main board component layout, etc. I've zipped several of these files and uploaded the zip file to my ftp site. You can download the zip file by typing in the following link in your browser command line. NOTE: This command is VERY CASE-SENSITIVE, so make sure you get it right.

ftp.grahampearson.com/SDConvertible/SDDistributionFiles.zip

Let me know if you need anything else.
Graham

[g1]

That link just gave the newsletter, but as you say, it must be typed into the address bar completely. Or copy and paste this:
ftp.grahampearson.com/SDConvertible/SDDistributionFiles.zip

[pslebow]

Thanks Graham! What a treasure trove!

It seems on my SD amp the effects loop is inserted before the volume and tone stack. I've seen some cryptic posts alluding to revisions in the design. I thought I could insert a line level into the effects return but found the output to the speakers was controlled by all the pre-amp pots. Inserting at grid to V2 (R28 on your layout) does the trick. Can feed my amp plugin outputs via my audio interface output directly to the power section of the SD.

On a business trip to SF about 20 years ago I actually stopped by the SD facility in Santa Barbara asking about the amp. To my surprise, Seymour came out to give me a personal tour. We had a long conversation about the impacts on guitar tone. Curiously he thought it was all in the wood!

Thanks again
Paul

[pslebow]

FWIW, Ive attached a photo of my amp circuit board to go with the layout.

[loudthud]

Seymour used to come to Guitar shows in Texas. I talked with him several times. One time we discussed the plastic used on little tube modules for a Convertible Amp that would twist and warp because of the heat.(supplier issue) Another time he brought a winding machine in an Anvil flight case and wound me a pair of P90 pickups for my Les Paul Pro. Great Guy !

[pslebow]

Yes, he was unassuming and unpretentious, and he knew what he was talking about.

[Helmholtz]

I once met Seymour in the early 80s at the Frankfurt Musikmesse.
Nice guy. We talked a bit about pickups and he offered to rewind me some '67 Strat PUs.
Which he did later.
Also gave me a chance to try the Convertible.
I asked him why he uses a tube rectifier with this 100W amp.
His answer was that he only likes amps with tube rectifiers.
My point is that a 5U4GB is specified for a max. sustained current of 275mA, while the four EL34s draw more than 400mA of plate current at full output.

BTW, the Vari-power circuit acts like an (active) crossline-MV.

[GrahamPearson]

I've owned several SD Convertibles, as well as the matching extension cab. I've come to prefer the earlier versions of this amp. Earlier versions have the humbucker symbol to the left of the SD nameplate and a Celestion G12K-85 speaker. The Service Bulletin, one of the files in the zip I linked in my previous post, recommends modifications to these earlier versions. I'm down to owning just one of these earlier versions and I've applied all of the recommended mods. It's one of the best sounding, and certainly the heaviest, amps I own. I'm sure the excellent tone is due to all that iron in the output transformer. Coupled with some good preamp modules, these amps are truly versatile. Recommended accessories: some robust casters or a stout hand cart.

[pslebow]

[QUOTE=GrahamPearson;n1007471]I've owned several "... The Service Bulletin, one of the files in the zip I linked in my previous post, recommends modifications to these earlier versions....."

Graham - I didn't see the service bulletin in your previous previous post. Is it somewhere else?

Do you know if the effects loop is routed before the preamp stage as it seems to be on my amp? The schematic indicates it goes to the input of the power amp section instead.

Thx
Paul

[GrahamPearson]

Hey Paul: If you look back to a couple of posts on this topic on 11/22/24, there's a link to a zip file you can download. One of the files in this zip is named "Seymour Duncan 100 Watt Convertible Service Bulletin 87-06-17.pdf". This is where you'll find the Service Bulletin. I don't know how to answer your question about the effects loop and its position in the signal chain.